Ceramic substrate and method of manufacturing the same

ABSTRACT

A ceramic substrate is provided that includes a ceramic substrate main body having a principal surface, and a connecting terminal portion disposed on the principal surface of the ceramic substrate main body that is capable of being connected to another component via solder. The connecting terminal portion includes a copper layer and a coating metal layer covering a surface of the copper layer. The ceramic substrate includes a contact layer disposed between the ceramic substrate main body and the copper layer. The contact layer includes one of a nickel-chromium alloy, chromium, molybdenum, and palladium, and is set back from a side surface of the copper layer in a substrate plane direction.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based on Japanese Patent Application No. 2012-277275filed with the Japan Patent Office on Dec. 19, 2012, the entire contentof which is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present disclosure relates to a ceramic substrate for mounting acomponent such as a light-emitting diode and a method of manufacturingthe ceramic substrate.

2. Description of Related Art

Light-emitting diodes (LEDs) are well known light-emitting elements. Inrecent years, a high-brightness blue LED has been put into practicaluse. The blue LED can be therefore combined with red and green LEDs toobtain high-brightness white light, facilitating the development of alight bulb or an automobile headlight using these three color LEDs. Ingeneral, LEDs have the advantage of smaller electric power consumption.Thus, the use of LEDs in headlights can reduce battery load. LEDs alsohave the advantage of long operating life, thereby being expected to beapplied in lighting fixtures, such as fluorescent lamps and light bulbs.For using LEDs in the above applications, high performance of a LEDpackage is an important factor in maximizing the advantages of the LEDs.In this respect, a ceramic package may be suitable for mounting LEDsbecause of its superior properties such as durability, heat resistance,corrosion resistance, and heat dissipation, compared with, for example,an organic package.

The ceramic package includes a ceramic substrate having an insulatorpart and a conductor part. The insulator part is made of, for example,an alumina-based ceramic material. The conductor part is made of a metal(such as tungsten or molybdenum) that can be co-fired with alumina.Further, a principal surface of the ceramic substrate has a connectingterminal portion for connection with the LED. The connecting terminalportion includes a copper layer made of copper and a metal layer (suchas a nickel layer or a gold layer) covering the copper layer, which aresuccessively stacked by any technique well known in the art (such as asputtering or plating technique). The copper layer of the connectingterminal portion has poor adhesion property to the ceramic layer. Thus,a contact layer of titanium is formed as an under layer for the copperlayer to improve the adhesion property of the connecting terminalportion (see, for example, JP-A-2010-223849).

BRIEF SUMMARY OF THE INVENTION

A ceramic substrate includes a ceramic substrate main body having aprincipal surface, and a connecting terminal portion disposed on theprincipal surface of the ceramic substrate main body and capable ofbeing connected to another component via solder. The connecting terminalportion includes a copper layer and a coating metal layer covering asurface of the copper layer. The ceramic substrate includes a contactlayer disposed between the ceramic substrate main body and the copperlayer. The contact layer includes one of a nickel-chromium alloy,chromium, molybdenum and palladium, and is set back from a side surfaceof the copper layer in a substrate plane direction.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view of a ceramic substrateaccording to an embodiment;

FIG. 2 is an enlarged cross-sectional view of a front surface-sideterminal portion;

FIG. 3 is a planar view of a rear surface-side terminal portion of asubstrate viewed from a rear surface side thereof;

FIG. 4 is a diagram illustrating a step of forming a through-hole;

FIG. 5 is a diagram illustrating a step of forming a via conductor and acastellation;

FIG. 6 is a diagram illustrating a step of forming a conductor layer anda wiring conductor portion;

FIG. 7 is a diagram illustrating a step of firing a ceramic substratemain body;

FIG. 8 is a diagram illustrating a step of forming a protection layer;

FIG. 9 is a diagram illustrating a step of forming a contact layer;

FIG. 10 is a diagram illustrating a step of forming a plating resist.

FIG. 11 is a diagram illustrating a step of forming a copper layer;

FIG. 12 is a diagram illustrating a step of peeling a plating resist;

FIG. 13 is a diagram illustrating a step of etching a contact layer; and

FIG. 14 is a diagram illustrating a step of forming a coating metallayer.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS OF THE INVENTION

In the following detailed description, for purpose of explanation,numerous specific details are set forth in order to provide a thoroughunderstanding of the disclosed embodiments. It will be apparent,however, that one or more embodiments may be practiced without thesespecific details. In other instances, well-known structures and devicesare schematically shown in order to simplify the drawing.

A ceramic package is formed by, for example, connecting a LED to aconnecting terminal portion of a ceramic substrate by soldering. Whenthe package is used in a high-temperature and high-humidity environment(such as at a temperature of 85° C. and a humidity of 85%), a solderingflux composition (active component) makes the package have a corrodedinterface between a copper layer and a titanium layer, which is in closecontact with each other, in a connecting terminal portion thereof. Suchcorrosion leads to an open failure at the connecting terminal portion.

At the connecting terminal portion of the ceramic package, a componentother than the LED, such as an IC chip, may be soldered. In this case, asimilar problem of open failure is also caused by corrosion when theceramic package is used in high-temperature and high-humidityenvironment.

An object of the present disclosure is to provide a ceramic substratethat can prevent a connecting terminal portion thereof from beingcorroded, and that has excellent connection reliability. Another objectof the present disclosure is to provide a method of manufacturing theceramic substrate.

A ceramic substrate in an embodiment of the present disclosure (theceramic substrate) includes a ceramic substrate main body having aprincipal surface, and a connecting terminal portion disposed on theprincipal surface of the ceramic substrate main body that can beconnected to another component via solder. The connecting terminalportion includes a copper layer and a coating metal layer covering asurface of the copper layer. The ceramic substrate includes a contactlayer disposed between the ceramic substrate main body and the copperlayer. The contact layer includes one of a nickel-chromium alloy,chromium, molybdenum and palladium, and is set back from a side surfaceof the copper layer in a substrate plane direction.

In the present ceramic substrate, the contact layer is disposed betweenthe ceramic substrate main body and the copper layer of the connectingterminal portion. Thus, a sufficient contact strength can be ensuredbetween the ceramic substrate main body and the connecting terminalportion. The contact layer of the present ceramic substrate is set backfrom the side surface of the copper layer in the substrate planedirection. Thus, when the other component is soldered to the connectingterminal portion, the soldering flux composition of the solder tends toeasily come into contact with the interface of the contact layer and thecopper layer. In the present ceramic substrate, the contact layercontains one of a nickel-chromium (Ni—Cr) alloy, chromium (Cr),molybdenum (Mo), and palladium (Pd). These metals have better corrosionresistance against the soldering flux composition in the solder thantitanium (Ti). Accordingly, when another component is soldered to theconnecting terminal portion of the present ceramic substrate, corrosiondue to the soldering flux composition as would result in theconventional art can be suppressed. As a result, open failure in theconnecting terminal portion can be avoided. Further, the connectionreliability of the ceramic substrate can be increased. The coating metallayer may contain at least nickel, and may further contain nickel andgold. The coating metal layer may further contain nickel, palladium, andgold.

The ceramic substrate may include a metallized metal layer disposed onthe principal surface of the ceramic substrate main body. The metallizedmetal layer may be coated with a protection layer for protecting from anetching solution for etching the contact layer, and at least a portionof the contact layer may be formed on the protection layer. Moreover, inthe ceramic substrate, a part of the metallized metal layer coated withthe protection layer may be extended from a projected area of theconnecting terminal portion.

At the time of manufacturing the ceramic substrate, the contact layer isformed as an underlayer of the connecting terminal portion throughsputtering and etching steps, for example. A part of the metallizedmetal layer may be extended beyond the projected area of the connectingterminal portion. In this case, the portion of the contact layerextended and exposed from the connecting terminal portion is removed byetching, whereby the contact layer is formed between the copper layerand the ceramic substrate main body. In this case, by coating themetallized metal layer with the protection layer prior to forming thecontact layer, corrosion of the metallized metal layer due to theetching solution for the contact layer can be avoided. As a result, theconnection reliability of the ceramic substrate can be ensured.

The present ceramic substrate may include an end-face through-holeconductor of a metallized metal disposed on a side surface of theceramic substrate main body, and a surface of the end-face through-holeconductor may be coated with the protection layer. In this way, too,corrosion of the metallized metal of the end-face through-hole conductordue to the etching solution for the contact layer can be avoided. Thus,the connection reliability of the ceramic substrate can be increased.

Further, in the present ceramic substrate, on the principal surface ofthe ceramic substrate main body, a wiring conductor portion includingthe metallized metal layer and connecting the connecting terminalportion with the end-face through-hole conductor may be disposed, and asurface of the wiring conductor portion may also be coated with theprotection layer. In this way, too, corrosion of the metallized metallayer of the wiring conductor portion due to the etching solution forthe contact layer can be avoided. Thus, the connection reliability ofthe ceramic substrate can be increased.

In the present ceramic substrate, the contact layer may be set back fromthe side surface of the copper layer such that a gap is formed betweenthe copper layer and the ceramic substrate main body, and the coatingmetal layer may be extended into the gap. In this case, a surface of thecopper layer can be reliably coated with the coating metal layer.Further, the outer surface of the contact layer is oxidized at the timeof manufacturing the present ceramic substrate. Thus, the outer surfaceof the contact layer is not coated with the coating metal layer, so thatthe interface of the contact layer and the copper layer tends to beeasily corroded. However, in the present ceramic substrate, thecorrosion at the interface due to the soldering flux composition can besuppressed. Accordingly, the connection reliability of the ceramicsubstrate can be ensured.

In the present ceramic substrate, the contact layer has a thickness of0.05 μm or more and 0.5 μm or less. By thus forming the contact layerwith an appropriate thickness, a sufficient adhesion property can beensured between the contact layer and the copper layer of the connectingterminal portion.

In the present ceramic substrate, the protection layer coating themetallized metal layer has a thickness of 0.8 μm or more and 2.5 μm orless. If the thickness of the protection layer is less than 0.8 μm,protection of the metallized metal layer against the etching solutionmay become insufficient. If the thickness of the protection layer ismore than 2.5 μm, the protection layer may be expanded by sintering andthe like, making the connecting terminal portion to be readily peeled.By forming the protection layer with the thickness of 0.8 μm or more and2.5 μm or less, the above problems can be avoided. As a result, theconnection reliability of the ceramic substrate can be ensured.

Specific examples of the protection layer include a nickel-plated layerand a gold plated layer. With the nickel-plated layer or the gold platedlayer, a sufficient adhesion property with the metallized metal layercan be ensured, and they are not removed by the etching of the contactlayer. Thus, the protection layer including a nickel-plated layer or agold plated layer can reliably protect the metallized metal layer. Whena nickel-plated layer is formed as the protection layer, the materialcost can be reduced compared with the gold plated layer. As a result,the manufacturing cost of the ceramic substrate can be decreased.

The ceramic substrate main body may have a multilayer structure. Namely,in the ceramic substrate main body, a plurality of ceramic insulatinglayers including a ceramic material and a plurality of conductor layersincluding a metallized metal layer may be stacked. In the ceramicinsulating layer, a via conductor including a metallized metal may beformed. The via conductor may be electrically connected to theconnecting terminal portion. In this way, in the present ceramicsubstrate, wiring patterns can be highly integrated. Thus, a pluralityof types of components can be mounted on the present ceramic substrate.

For the ceramic insulating layer, a sintered material of hightemperature fired ceramics may be preferably used. Examples of thesintered material of high temperature fired ceramics include alumina,aluminum nitride, boron nitride, silicon carbide, and silicon nitride.When alumina is used as the ceramic material for the ceramic insulatinglayer, a ceramic substrate having excellent product reliability inhigh-temperature and high-humidity environment can be manufactured.

The metallized metal layer and the via conductor may be formed byapplying a conductor paste containing a metal powder by a conventionallyknown process (such as metallization printing) and then performingfiring. When the metallized metal layer, the via conductor, and theceramic insulating layer are formed by co-firing process, the metalpowder in the conductor paste has a higher melting point than the firingtemperature of the ceramic insulating layer. For example, when theceramic insulating layer contains so-called high temperature firedceramics (such as alumina), nickel (Ni), tungsten (W), molybdenum (Mo),manganese (Mn), or an alloy thereof may be selected as the metal powderin the conductor paste.

Examples of the component soldered to the connecting terminal portioninclude electronic components such as an LED, a resistor, a capacitor,an inductor, and a semiconductor integrated-circuit element. The presentceramic substrate with the LED connected to the connecting terminalportion is used as a lighting apparatus, such as an outdoor lightingapparatus or an automobile headlight. In this case, the present ceramicsubstrate is used for a long period in high-temperature andhigh-humidity environment. Thus, the development of corrosion at theinterface of the contact layer and the connecting terminal portion aswould occur in the conventional art leads to a decrease in strength atthe interface, potentially causing open failure (terminal peeling) andthe like. On the other hand, in the present ceramic substrate, thedevelopment of corrosion at the interface of the contact layer and theconnecting terminal portion can be prevented even in high-temperatureand high-humidity environment. Thus, product reliability can be ensuredfor a long period.

A method of manufacturing the ceramic substrate in an embodiment of thepresent disclosure includes: a firing step of forming the ceramicsubstrate main body and the metallized metal layer; a protectionlayer-forming step of forming the protection layer by performing nickelplating on the metallized metal layer exposed on the principal surfaceside of the ceramic substrate main body; a contact layer-forming step offorming the contact layer on a surface of the protection layer and onthe principal surface of the ceramic substrate main body; a copperlayer-forming step of forming the copper layer of the connectingterminal portion on a surface of the contact layer by performing copperplating; an etching step of removing the contact layer exposed on theprincipal surface side of the ceramic substrate main body by etchingwhile protecting the metallized metal layer from corrosion due to theetching solution with the protection layer; and a coating metallayer-forming step of forming the coating metal layer on the surface ofthe copper layer by successively plating the surface of the copper layerwith nickel and gold or with nickel, palladium, and gold.

According to the present manufacturing method, the protectionlayer-forming step is performed prior to forming the contact layer inthe contact layer-forming step. In this step, the protection layer isformed by performing nickel plating on the metallized metal layerexposed on the principal surface side of the ceramic substrate mainbody. In the protection layer-forming step, sintering may be performedon the protection layer so as to increase the contact strength betweenthe metallized metal layer and the protection layer. Subsequently, thecontact layer-forming step and the copper layer-forming step areperformed successively. Thus, the contact layer and the copper layer areformed on the metallized metal layer via the protection layer.

In the etching step, the contact layer is etched to remove a part of thecontact layer exposed on the principal surface side of the ceramicsubstrate main body. As a result, the contact layer remains between theprincipal surface of the ceramic substrate main body and the copperlayer, while a part of the outer surface of the contact layer that isdisposed between the principal surface of the ceramic substrate mainbody and the copper layer is removed by etching. Thus, the contact layeris set back from the side surface of the copper layer in the substrateplane direction. In addition, the protection layer protects the surfaceof the metallized metal layer. Thus, the protection layer prevents theetching solution from causing corrosion of the metallized metal layer inthe etching step. Subsequently, in the coating metal layer-forming step,the coating metal layer is formed on the surface of the copper layer.Thus, the connecting terminal portion including the copper layer and thecoating metal layer is formed.

Thus, in the present ceramic substrate, the contact layer is formedbetween the principal surface of the ceramic substrate main body and thecopper layer of the connecting terminal portion. The contact layercontains one of a nickel-chromium alloy, chromium, molybdenum, andpalladium. The contact layer has better corrosion resistance against thesoldering flux composition than titanium. Accordingly, when the othercomponent is soldered to the connecting terminal portion, corrosion dueto the soldering flux composition as would be caused in the contactlayer of titanium according to the conventional art can be suppressed.As a result, open failure in the connecting terminal portion can beavoided, whereby the connection reliability of the ceramic substrate canbe increased.

In the following, a ceramic substrate according to an embodiment of thepresent disclosure will be described with reference to the drawings.

As illustrated in FIG. 1, a ceramic substrate 10 according to thepresent embodiment includes a ceramic substrate main body 13 in the formof a rectangular plate. The ceramic substrate main body 13 has principalsurfaces that include a substrate front surface 11 and a substrate rearsurface 12. On the substrate front surface 11 side, an LED 15 ismounted. The ceramic substrate main body 13 has a multilayer structure.Namely, the ceramic substrate main body 13 includes two ceramicinsulating layers 21 and 22 and a conductor layer 23, which are stackedon one another. The insulating layers 21 and 22 each contain a ceramicmaterial, and the conductor layer 23 includes a metallized metal layer.The ceramic insulating layers 21 and 22 are sintered materials eachcontaining alumina as a ceramic material. The conductor layer 23includes, for example, tungsten, molybdenum, or an alloy thereof.

The ceramic insulating layers 21 and 22 of the ceramic substrate mainbody 13 have via holes 25 extending in a thickness direction. Viaconductors 26 are formed in the respective via holes 25. The viaconductor 26 includes, for example, a metallized metal of tungsten,molybdenum, or an alloy thereof.

The ceramic substrate 10 further includes two front surface-sideterminal portions 31 (connecting terminal portions) disposed on thesubstrate front surface 11 side of the ceramic substrate main body 13thereof. The front surface-side terminal portions 31 are connected tothe LED 15 (other component). Specifically, the front surface-sideterminal portions 31 are disposed immediately above the via conductors26, respectively. In other words, the front surface-side terminalportions 31 are disposed on the surface of the upper ends of the viaconductors 26, and are electrically connected to the via conductors 26,respectively. Each front surface-side terminal portion 31 has a widthgreater than the diameter of the corresponding via conductor 26. Thefront surface-side terminal portions 31 are formed to entirely cover theupper ends of the via conductors 26, respectively.

The ceramic substrate main body 13 further includes two rearsurface-side terminal portions 32 (connecting terminal portions) on therear surface 12 side thereof. The rear surface-side terminal portions 32are connected to an external substrate (another component) (not shown).One of the rear surface-side terminal portions 32 (in FIG. 1, the rightside terminal portion) is disposed on the surface of the lower end ofthe corresponding via conductor 26 to make an electrical connectiontherebetween. The other of the rear surface-side terminal portions 32(in FIG. 1, the left side terminal portion) is connected not to the viaconductors 26 but to a wiring conductor portion 34 (conductor layer)disposed on the substrate rear surface 12. Like the conductor layer 23,the wiring conductor portion 34 includes a metallized metal layer oftungsten, molybdenum, or an alloy thereof.

The ceramic substrate main body 13 includes a side surface 16 in which arecessed portion 36 with semi-circular cross section is formed. On thesurface of the recessed portion 36, a castellation 37 (end-facethrough-hole conductor) is disposed. Like the via conductors 26, thecastellation 37 includes a metallized metal of tungsten, molybdenum, oran alloy thereof. The castellation 37 is connected to the wiringconductor portion 34 on the substrate rear surface 12. The castellation37 is also connected to a conductor layer 23 disposed between theceramic insulating layer 21 and the ceramic insulating layer 22. Theconductor layer 23 is connected to the front surface-side terminalportion 31 via the via conductor 26.

As illustrated in FIGS. 1 and 2, the front surface-side terminal portion31 includes a copper layer 41 and a coating metal layer 42 that coversthe surface of the copper layer 41. The copper layer 41 of the frontsurface-side terminal portions 31 includes a copper plated layer. Thecoating metal layer 42 includes a nickel-plated layer and a gold platedlayer. Between the ceramic substrate main body 13 and the copper layer41 of the front surface-side terminal portions 31, a contact layer 43including molybdenum is disposed. The contact layer 43 is a metal layerwith an adhesion property superior to that of the copper layer 41 withrespect to the ceramic substrate main body 13 (ceramic insulating layers21 and 22). The contact layer 43 may include one of a nickel-chromiumalloy, chromium, and palladium, other than molybdenum. The contact layer43 has a thickness of 0.05 μm or more and 0.5 μm or less. The contactlayer 43 is formed by a process conventionally known, such as sputteringor CVD.

According to the present embodiment, the contact layer 43 is set backfrom the side surface 41 a of the copper layer 41 of the frontsurface-side terminal portions 31 in a substrate plane direction. Thecontact layer 43 is set back from the side surface 41 a of the copperlayer 41. Thus, a gap is formed between the copper layer 41 and thesubstrate front surface 11. The coating metal layer 42 extends into thegap. The outer surface of the contact layer 43 is oxidized and thereforeis not covered with the coating metal layer 42. Further, according tothe present embodiment, a nickel-plated layer 45 is disposed between thecontact layer 43 and the metallized metal of the via conductors 26. Thenickel-plated layer 45 has a thickness of 0.8 μm or more and 2.5 μm orless, for example.

As descried above, the rear surface-side terminal portions 32 is formedon the substrate rear surface 12 of the ceramic substrate main body 13.The rear surface-side terminal portions 32 have a layer structuresimilar to the layer structure of the front surface-side terminalportions 31. Namely, the rear surface-side terminal portions 32 includethe copper layer 41 and the coating metal layer 42 covering the surfaceof the copper layer 41. The contact layer 43 including molybdenum isdisposed between the ceramic substrate main body 13 and the copper layer41 of the rear surface-side terminal portions 32. The contact layer 43is set back from the side surface 41 a of the copper layer 41 of therear surface-side terminal portions 32 in the substrate plane direction.The contact layer 43 is set back from the side surface 41 a of thecopper layer 41. Thus, a gap is formed between the copper layer 41 andthe substrate rear surface 12. The coating metal layer 42 extends intothe gap. The outer surface of the contact layer 43 is oxidized andtherefore is not coated with the coating metal layer 42. Thenickel-plated layer 45 is disposed between the contact layer 43 and themetallized metal of the via conductor 26.

On the substrate rear surface 12 of the ceramic substrate main body 13,the surface of the metallized metal layer of the wiring conductorportion 34 is coated with the nickel-plated layer 45. The nickel-platedlayer 45 is a protection layer for protecting the wiring conductorportion 34 from etching solution with which the contact layer 43 isetched. According to the present embodiment, a part of the wiringconductor portion 34 (metallized metal layer) coated with thenickel-plated layer 45 extends beyond a projected area R1 of the rearsurface-side terminal portion 32 (see FIG. 3). In FIG. 3, the areainside the outline of the rear surface-side terminal portion 32constitutes the projected area R1 of the rear surface-side terminalportion 32. As illustrated in FIG. 1, the nickel-plated layer 45 is alsodisposed between the metallized metal layer of the wiring conductorportion 34 and the contact layer 43 at the rear surface-side terminalportion 32 connected to the wiring conductor portion 34.

The surface of the metallized metal of the castellation 37 formed on theside surface 16 of the ceramic substrate main body 13 is also coveredwith the nickel-plated layer 45 (protection layer). Further, a surfaceof the nickel-plated layer 45 (protection layer) that is on the surfaceof the wiring conductor portion 34 exposed from the rear surface-sideterminal portion 32 and on the surface of the castellation 37 is coatedwith the coating metal layer 42 (nickel-plated layer and gold platedlayer).

A method of manufacturing the ceramic substrate 10 according to thepresent embodiment will be described. The ceramic substrate 10 accordingto the present embodiment is manufactured by a multi-piece process.

First, an alumina powder as ceramic material, an organic binder, asolvent, a plasticizer and the like are mixed to prepare slurry. Theslurry is formed into a sheet by a process conventionally known (such asdoctor blade method or calendar roll method). In this way, two ceramicgreen sheets are prepared.

Then, through-holes 53 and 54 are formed at a plurality of locations inthe ceramic green sheets 51 and 52 by punching (see FIG. 4). Thethrough-holes 53 and 54 penetrate the ceramic green sheets 51 and 52 intheir thickness direction. The through-holes 53 and 54 may be formed bya process other than punching, such as laser drilling.

The through-holes 53 in the ceramic green sheets 51 and 52 are holeportions for forming the via conductors 26. The through-holes 54 arehole portions for forming the castellation 37. Namely, after ceramicfiring, the through-holes 53 form the via holes 25, and a part of thethrough-holes 54 forms the recessed portion 36.

Conductor portions are formed in the through-holes 53 and 54,respectively. More specifically, the through-holes 53 are initiallyfilled with an electrically conductive paste containing tungsten ormolybdenum by using a conventionally known paste printing apparatus.Thus, un-fired via conductor portions 55 to be formed into the viaconductors 26 are formed (see FIG. 5). Namely, the un-fired viaconductor portions 55 are formed by completely filling the through-holeswith the electrically conductive paste. Then, castellation printing isperformed to attach the electrically conductive paste containingtungsten or molybdenum onto the inner peripheral surfaces of thethrough-holes 54. Thus, conductor portions 56 for the un-firedcastellation to be formed into the castellation 37 are formed (see FIG.5). The through-holes 54 may not be completely filled with theelectrically conductive paste. The center of the conductor portions 56for un-fired castellation is hollowed. The castellation printing may beperformed after the un-fired via conductor portions 55 are formed asdescribed above. Alternatively, the un-fired via conductor portions 55may be formed after the castellation printing.

Then, un-fired conductor portions 57 are formed on the ceramic greensheets 51 and 52 by screen-printing (see FIG. 6). Here, an electricallyconductive paste is printed on surfaces (lower surfaces in FIG. 6) ofthe ceramic green sheets 51 and 52 by using a mask (not illustrated). Inthis way, the un-fired conductor portions 57 are patterned. The un-firedconductor portions 57 are later formed into the conductor layer 23 andthe wiring conductor portion 34. Subsequently, the ceramic green sheets51 and 52 are heated to a predetermined temperature, whereby theun-fired conductor portions 55, 56, and 57 formed on the ceramic greensheets 51 and 52 are dried.

The ceramic green sheet 51 and the ceramic green sheet 52 are thenlaminated, and a predetermined load is applied to the resultantlaminated body in a thickness direction by using a conventionally knownlaminating apparatus, whereby the ceramic green sheets 51 and 52 arecompressed and integrated. Thus, an un-fired ceramic laminated body isformed.

Subsequently, the un-fired ceramic laminated body is heated to apredetermined temperature (such as approximately 1500° C. to 1800° C.)such that the alumina can be sintered (firing step). Through the firingstep, the ceramic green sheets 51 and 52 are sintered. As a result, aceramic substrate main body 60 including the integrated ceramicinsulating layers 21 and 22 is obtained (see FIG. 7). At the same time,the metallized metal layer of the conductor layer 23 and the wiringconductor portion 34, and the metallized metal of the via conductors 26and the through-hole conductors 37A are formed by the sintering of theelectrically conductive paste.

Next, nickel electroplating is performed in a protection layer-formingstep. As a result, in the ceramic substrate main body 60, anickel-plated layer 45 is formed on the surface of the metallized metallayer of the wiring conductor portion 34, and on the surface of themetallized metal of the via conductors 26 and the through-holeconductors 37A (see FIG. 8). The resulting nickel-plated layer 45 has athickness of 0.8 μm or more and 2.5 μm or less. Subsequently, theceramic substrate main body 60 is heated to a temperature ofapproximately 850° C. to sinter the nickel-plated layer 45.

Next, as illustrated in FIG. 9, molybdenum sputtering is performed toform the contact layer 43 on the surface of the nickel-plated layer 45and the substrate front surface 11 and the substrate rear surface 12 ofthe ceramic substrate main body 60 (contact layer-forming step). Theresulting contact layer 43 has a thickness of 0.05 μm or more and 0.5 μmor less. Further, copper sputtering is performed to form a coppersputtered layer (not illustrated) on the surface of the contact layer43.

Subsequently, a copper layer-forming step is performed. Specifically, aphotosensitive plating resist material is applied onto the substratefront surface 11 and the substrate rear surface 12 of the ceramicsubstrate main body 60. On the plating resist material, an exposing maskwith a predetermined mask pattern is disposed, and the plating resistmaterial is exposed via the exposing mask. The exposed plating resistmaterial is then developed to form a plating resist 61 (see FIG. 10).Then, copper electroplating is performed to form the copper layer 41 forthe front surface-side terminal portions 31 and the rear surface-sideterminal portions 32 on the surface of the contact layer 43 (see FIG.11).

Then, surface-conditioning polishing is performed to grind the surfaceof the plating resist 61 and the end face of the copper layer 41,whereby the height of each copper layer 41 is adjusted to apredetermined height (such as on the order of 100 μm). Then, the platingresist 61 on the substrate front surface 11 and on the substrate rearsurface 12 is peeled by contacting a peeling solution (see FIG. 12).Subsequently, copper etching is performed to remove the copper sputteredlayer (not illustrated) exposed on the substrate front surface 11 andthe substrate rear surface 12. Further, as illustrated in FIG. 13,molybdenum etching is performed to remove the contact layer 43 exposedon the substrate front surface 11 and the substrate rear surface 12(etching step). At this time, the nickel-plated layer 45 formed on thesurface of the metallized metal layer of the wiring conductor portion 34and on the surface of the metallized metal of the through-holeconductors 37A functions as a protection layer against the etchingsolution for the contact layer 43. Thus, the etching solution can beprevented from causing corrosion of the metallized metal layer of thewiring conductor portion 34 and corrosion of the metallized metal of thethrough-hole conductors 37A.

In the contact layer 43 etching step, the outer surface of the contactlayer 43 disposed between the principal surfaces of the ceramicsubstrate main body 60 (the substrate front surface 11 and the substraterear surface 12) and the copper layer 41 is partially removed byetching. Thus, the contact layer 43 is set back from the side surface 41a of the copper layer 41 in a substrate plane direction.

Next, the ceramic substrate main body is heated to a temperature of 500°C. (heating process). This heating process enhances the adhesionproperty between the contact layer 43 and the nickel-plated layer 45. Inaddition, this heating process enhances the adhesion property betweenthe copper layer 41 and the contact layer 43.

Next, as illustrated in FIG. 14, a coating metal layer-forming step isperformed. In the coating metal layer-forming step, nickel plating andgold plating (specifically, nickel electroplating and goldelectroplating) are successively performed on the surfaces of the copperlayer 41 on the front surface-side terminal portions 31 and on the rearsurface-side terminal portions 32, and on the surfaces of the metallizedmetal layer of the wiring conductor portion 34 and the metallized metalof the through-hole conductors 37A. Thus, the coating metal layer 42 isformed on these surfaces.

The ceramic substrate main body 60 obtained through the above steps is amulti-piece substrate including a plurality of product areas arrangedvertically and horizontally along the planar direction. The multi-piecesubstrate main body 60 is divided in a dividing step, whereby aplurality of the ceramic substrates 10 illustrated in FIG. 1 can besimultaneously obtained. Further, in the dividing step, the ceramicsubstrate main body 60 is divided at the positions of the through-holeconductors 37A (positions indicated by dashed lines in FIG. 14). In thisway, the castellation 37 (end-face through-hole conductor) exposed onthe side surface 16 is formed.

The inventors performed a product reliability evaluation test on theceramic substrate 10 manufactured by the above manufacturing method.Specifically, the rate of change of electric resistance and the adhesionproperty of the connecting terminal portion (front surface-side terminalportions 31) in a high temperature (85° C.) and high humidity (85%)environment were evaluated. The evaluation results are shown in Tables 1and 2 below.

In the evaluation test, the first to the fourth examples of the ceramicsubstrate 10 were fabricated while varying the forming material of thecontact layer 43. In the first example, the contact layer 43 was formedby sputtering a nickel-chromium (Ni—Cr) alloy. In the second example,the contact layer 43 was formed by sputtering chromium (Cr). In thethird example, the contact layer 43 was formed by sputtering palladium(Pd). In the fourth example, the contact layer 43 was formed bysputtering molybdenum (Mo). Further, the ceramic substrate according toa first conventional example was prepared and subjected to theevaluation test. In the first conventional example, the contact layerwas formed by sputtering titanium (Ti).

The evaluation test of the rate of change of electric resistance wasperformed as follows: The rear surface-side terminal portions 32 of theceramic substrate 10 were surface-mounted on a resin circuit substrate(PCB) via solder. The front surface-side terminal portions 31 of theceramic substrate 10 were electrically connected (short-circuited) by acopper wire and the like. Further, in the resin circuit substrate,copper wires were connected to connecting terminals connected to therear surface-side terminal portions 32 via a wiring pattern.

Subsequently, the ceramic substrate 10 mounted on the resin circuitsubstrate was placed in an environmental testing apparatus (thehigh-temperature/high-humidity testing apparatus PL-1 KP from EspecCorp.). The copper wires connected to the resin circuit substrate weredrawn outside the testing apparatus external, and a four-terminalmeasuring apparatus (the 3227 mΩ Hitester from Hioki E.E. Corporation)was connected to the copper wires drawn outside the testing apparatus.With the measuring apparatus, the resistance value of the ceramicsubstrate 10 was measured. During the measurement of the resistancechange rate in the evaluation test, the resistance value of the ceramicsubstrate 10 was measured after 500, 750, and 1000 hours of processingtime of the high-temperature/high-humidity test following the start ofoperation of the environmental testing apparatus. The resistance changerate is the rate of change from the initial resistance value at thestart of testing and is calculated by the following calculation formula.Resistance change rate (%)=100×(measured value−initial resistancevalue)/initial resistance value

TABLE 1 Contact Processing time (hours) layer 0 500 750 1000 Firstconventional Ti 0% 0% +50%  +100%    example First example NiCr 0% 0% 0%0% Second example Cr 0% 0% 0% 0% Third example Pd 0% 0% 0% 0% Fourthexample Mo 0% 0% 0% 0%

As shown in Table 1, in the ceramic substrate according to the firstconventional example with the contact layer containing titanium, theresistance value was increased after 750 hours of processing time of thehigh-temperature/high-humidity test, where the resistance change ratewas 50%. Further, in the first conventional example, the resistancechange rate became 100% (open failure) after 1000 hours of processingtime of the high-temperature/high-humidity test. On the other hand, inthe ceramic substrate 10 according to the first to the fourth examples,the resistance change rate remained at 0% even after 1000 hours of thehigh-temperature/high-humidity test, and no deterioration in electriccharacteristics was observed.

The evaluation test for the adhesion property of the connecting terminalportion was conducted as follows: To the front surface-side terminalportions 31 of the ceramic substrate 10, a flux material (such asES-1061SP-2 from Senju Metal Industry Co., Ltd.) was applied. Then, theceramic substrate 10 was placed in the environmental testing apparatus.The ceramic substrate 10 was taken out of the environmental testingapparatus after the elapse of predetermined times (500, 750, 1000, and1500 hours) in the high-temperature and high-humidity environment, andthe failure mode was confirmed by a shear test. In the shear test, byusing a shear tester (shear measuring device: the die shear tester DageSeries 4000 from Arctec), the front surface-side terminal portions 31were caused to fracture, and the fractured surface was analyzed. Thefailure mode includes interface failure and substrate failure. Theinterface failure is a failure of the front surface-side terminalportions 31 at the interface between the copper layer 41 of the frontsurface-side terminal portions 31 and the contact layer 43. Thesubstrate failure is a failure of the front surface-side terminalportions 31 at the ceramic portion inside the ceramic insulating layer21. The testing results for the respective ceramic substrates 10 areshown in Table 2.

TABLE 2 Contact Processing time (hours) layer 0 500 750 1000 1500 FirstTi Substrate Interface Interface Interface Interface conventionalfailure failure failure failure failure example First NiCr ↑ SubstrateSubstrate Interface Interface example failure failure failure failureSecond Cr ↑ ↑ Interface Interface Interface example failure failurefailure Third Pd ↑ ↑ Substrate Substrate Interface example failurefailure failure Fourth Mo ↑ ↑ ↑ ↑ Substrate example failure

As shown in Table 2, according to the first conventional example, whenthe high-temperature/high-humidity test was conducted for 500 hours, theadhesion property between the copper layer 41 and the contact layer 43deteriorated, and failure occurred at the interface of the copper layer41 and the contact layer 43. On the other hand, according to the firstto the fourth examples, in the 500 hours of thehigh-temperature/high-humidity test, no failure was caused at theinterface of the copper layer 41 and the contact layer 43. Thus, animprovement in the adhesion property between the copper layer 41 and thecontact layer 43 was confirmed. In particular, in the fourth example inwhich the contact layer 43 was formed by molybdenum, no failure occurredat the interface of the copper layer 41 and the contact layer 43 evenafter 1500 hours of the high-temperature/high-humidity test. Namely, itwas confirmed that the adhesion property of the contact layer 43 wasincreased even more in the fourth example.

Thus, according to the present embodiment, the following effects can beobtained.

-   -   (1) In the ceramic substrate 10 according to the present        embodiment, the contact layer 43 is disposed between the ceramic        substrate main body 13 and the copper layer 41 of the front        surface-side terminal portions 31 and the rear surface-side        terminal portions 32. The contact layer contains one of a        nickel-chromium (Ni—Cr) alloy, chromium (Cr), molybdenum (Mo),        and palladium (Pd). Thus, the contact strength between the        ceramic substrate main body 13 and the terminal portions 31 and        32 can be sufficiently ensured. Further, these metals contained        in the contact layer 43 have better corrosion resistance against        the soldering flux composition in solder than titanium (Ti).        Then, corrosion of the terminal portions 31 and 32 due to the        soldering flux composition can be suppressed in the case of        soldering the LED 15 to the front surface-side terminal portions        31 and in the case of soldering an external substrate to the        rear surface-side terminal portions 32 soldering flux        composition. Consequently, open failure in the terminal portions        31 and 32 can be avoided, and the connection reliability of the        ceramic substrate 10 can be increased.    -   (2) In the ceramic substrate 10 according to the present        embodiment, the metallized metal layer of the wiring conductor        portion 34 is coated with the nickel-plated layer 45. A part of        the wiring conductor portion 34 (metallized metal layer) is        extended beyond the projected area R1 of the rear surface-side        terminal portions 32. Further, the metallized metal of the        castellation 37 is also coated with the nickel-plated layer 45.        The nickel-plated layer 45 functions as a protection layer        against the etching solution for the contact layer 43. Thus, the        etching solution can be prevented from causing corrosion of the        metallized metal layer of the wiring conductor portion 34 and        corrosion of the metallized metal of the castellation 37. As a        result, the connection reliability of the ceramic substrate 10        can be ensured.    -   (3) In the ceramic substrate 10 according to the present        embodiment, the contact layer 43 is set back from the side        surface 41 a of the copper layer 41. The coating metal layer 42        extends into the gap at this portion. Thus, the surface of the        copper layer 41 can be reliably coated with the coating metal        layer 42.    -   (4) In the ceramic substrate 10 according to the present        embodiment, the thickness of the contact layer 43 is set to be        0.05 μm or more and 0.5 μm or less, for example. By thus forming        the contact layer 43 with an appropriate thickness, the adhesion        property between the contact layer 43 and the copper layer 41        can be sufficiently ensured. The thickness of the nickel-plated        layer 45 is set to be 0.8 μm or more and 2.5 μm or less, for        example. By forming the nickel-plated layer 45, the metallized        metal layer of the wiring conductor portion 34 and the        metallized metal of the castellation 37 can be reliably        protected from the etching solution for the contact layer 43.        Thus, the connection reliability of the ceramic substrate 10 can        be ensured.    -   (5) In the ceramic substrate 10 according to the present        embodiment, the LED 15 is surface-mounted on the front        surface-side terminal portions 31 via solder. The ceramic        substrate 10 is used for a long period in a high-temperature and        high-humidity environment, and yet in the ceramic substrate 10,        the progress of corrosion at the interface of the copper layer        41 and the contact layer 43 can be prevented. Thus, the product        reliability can be ensured.

The embodiment of the present disclosure may be modified as follows:

The ceramic substrate 10 according to the foregoing embodiment may beconfigured to mount a chip component other than the LED 15. For example,in the ceramic substrate 10, a through-hole is formed in the ceramicinsulating layer 21 disposed on the upper side, and the bottom of thethrough-hole is closed by the ceramic insulating layer 22 disposed onthe lower side, whereby a cavity (housing recessed portion) is formed.In the cavity, a chip such as a surge-resistant chip (chip component forsurge voltage protection) may be housed.

In the ceramic substrate 10, a connecting terminal portion for mountingthe surge-resistant chip may be formed at the bottom of the cavity.Further, a wiring pattern and/or a via conductor for connecting theconnecting terminal portion with the LED-mounting connecting terminalportion may be formed in the ceramic insulating layers 21 and 22. In theceramic substrate 10, like the LED-mounting connecting terminal portion,the connecting terminal portion for mounting the surge-resistant chipalso has a layered structure including the contact layer 43. Thus, theconnection reliability can be increased.

In the ceramic substrate 10 according to the present embodiment, thecastellation 37 is disposed on the side surface 16 of the ceramicsubstrate main body 13. However, the ceramic substrate according to thepresent disclosure may not include the castellation 37. The ceramicsubstrate 10 includes the two ceramic insulating layers 21 and 22. Theceramic substrate according to the present disclosure may include amultilayered wiring substrate with three or more ceramic insulatinglayers.

Technical concepts that may be grasped from the foregoing embodimentsare listed below.

-   -   (1) A ceramic substrate in an embodiment of the present        disclosure (the ceramic substrate) includes a ceramic substrate        main body having a principal surface, and a connecting terminal        portion disposed on the principal surface of the ceramic        substrate main body that is capable of being connected to        another component via solder. The connecting terminal portion        includes a copper layer and a coating metal layer covering a        surface of the copper layer. The ceramic substrate includes a        contact layer disposed between the ceramic substrate main body        and the copper layer. The contact layer includes one of a        nickel-chromium alloy, chromium, molybdenum and palladium, and        is set back from a side surface of the copper layer in a        substrate plane direction.

In the present ceramic substrate, on the principal surface of theceramic substrate main body, a wiring conductor portion including ametallized metal layer and connecting the connecting terminal portionand an end-face through-hole conductor may be disposed. The metallizedmetal layer may be coated with a protection layer. The protection layerprotects the metallized metal layer from an etching solution for etchingthe contact layer.

-   -   (2) In present ceramic substrate, the contact layer may be set        back from the side surface of the copper layer such that a gap        is formed between the copper layer and the ceramic substrate        main body. In the gap, the coating metal layer may be extended.    -   (3) In the present ceramic substrate, an outer surface of the        contact layer may not be coated with the coating metal layer.    -   (4) In the present ceramic substrate, the contact layer may have        a thickness of 0.05 μm or more and 0.5 μm or less.    -   (5) In the present ceramic substrate, the contact layer may        include a metal layer having a better corrosion resistance to a        soldering flux composition in the solder than titanium.    -   (6) In the present ceramic substrate, a metallized metal layer        may be disposed on the principal surface of the ceramic        substrate main body, and the metallized metal layer may be        coated with a protection layer. The protection layer protects        the metallized metal layer from an etching solution for etching        the contact layer. The protection layer may have a thickness of        0.8 μm or more and 2.5 μm or less.    -   (7) According to this configuration, the protection layer        coating the metallized metal layer may include a nickel-plated        layer.    -   (8) In the present ceramic substrate, a metallized metal layer        may be disposed on the principal surface of the ceramic        substrate main body. The metallized metal layer may contain        molybdenum. The contact layer may also contain molybdenum.    -   (9) In the present ceramic substrate, an LED may be connected to        the connecting terminal portion as the other component.    -   (10) In the present ceramic substrate, the ceramic substrate        main body may have a multilayer structure. Namely, in the        ceramic substrate main body, a plurality of ceramic insulating        layer including a ceramic material and a plurality of conductor        layers including a metallized metal layer may be stacked. The        ceramic insulating layer may include a via conductor containing        a metallized metal, and the via conductor may be electrically        connected to the connecting terminal portion.    -   (11) In this configuration, the ceramic material in the ceramic        substrate main body may be alumina.

The foregoing detailed description has been presented for the purposesof illustration and description. Many modifications and variations arepossible in light of the above teaching. It is not intended to beexhaustive or to limit the subject matter described herein to theprecise form disclosed. Although the subject matter has been describedin language specific to structural features and/or methodological acts,it is to be understood that the subject matter defined in the appendedclaims is not necessarily limited to the specific features or actsdescribed above. Rather, the specific features and acts described aboveare disclosed as example forms of implementing the claims appendedhereto.

What is claimed is:
 1. A ceramic substrate, comprising: a ceramicsubstrate main body having a principal surface; a connecting terminalportion disposed on the principal surface of the ceramic substrate mainbody for connection to a component via solder, the connecting terminalportion including a copper layer and a coating metal layer covering asurface of the copper layer; and a contact layer disposed between theceramic substrate main body and the copper layer, the contact layerincluding one of a nickel-chromium alloy, chromium, molybdenum, andpalladium, wherein the contact layer is set back from a side surface ofthe copper layer in a substrate plane direction such that a gap isformed between the copper layer and the ceramic substrate main body, andwherein the coating metal layer extends into the gap.
 2. The ceramicsubstrate according to claim 1, wherein the coating metal layer includesat least nickel.
 3. The ceramic substrate according to claim 1, whereinthe coating metal layer includes nickel and gold or includes nickel,palladium, and gold.
 4. A ceramic substrate comprising: a ceramicsubstrate main body having a principal surface; a metallized metal layerdisposed on the principal surface of the ceramic substrate main body, aprotection layer coated on the metallized metal layer for protecting themetallized metal layer from an etching solution; a contact layerincluding one of a nickel-chromium alloy, chromium, molybdenum, andpalladium, at least a portion of the contact layer formed on theprincipal surface of the ceramic substrate main body, and at leastanother portion of the contact layer formed on the protection layer; anda connecting terminal portion formed on the contact layer for connectionto a component via solder, the connecting terminal portion including acopper layer and a coating metal layer covering a surface of the copperlayer, wherein the contact layer is set back from a side surface of thecopper layer in a substrate plane direction such that a gap is formedbetween the copper layer and the ceramic substrate main body, andwherein the coating metal layer extends into the gap.
 5. The ceramicsubstrate according to claim 4, wherein a part of the metallized metallayer coated with the protection layer is extended from a projected areaof the connecting terminal portion.
 6. The ceramic substrate accordingto claim 4, further comprising: an end-face through-hole conductorincluding a metallized metal and disposed on a side surface of theceramic substrate main body, wherein a surface of the end-facethrough-hole conductor is coated with the protection layer.
 7. A methodof manufacturing the ceramic substrate according to claim 4, the methodcomprising: a firing step of forming the ceramic substrate main body andthe metallized metal layer; a protection layer-forming step of formingthe protection layer by performing nickel plating on the metallizedmetal layer exposed on the principal surface side of the ceramicsubstrate main body; a contact layer-forming step of forming the contactlayer on a surface of the protection layer and on the principal surfaceof the ceramic substrate main body; a copper layer-forming step offorming the copper layer of the connecting terminal portion on a surfaceof the contact layer by performing copper plating; an etching step ofremoving the contact layer exposed on the principal surface side of theceramic substrate main body by etching while protecting the metallizedmetal layer from corrosion due to the etching solution with theprotection layer; and a coating metal layer-forming step of forming thecoating metal layer on the surface of the copper layer by successivelyplating the surface of the copper layer with nickel and gold or withnickel, palladium, and gold.